U.S. patent application number 16/690369 was filed with the patent office on 2020-03-19 for photoelectric conversion element, and method and apparatus for manufacturing the same.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Takeshi Gotanda, Hyangmi Jung.
Application Number | 20200091451 16/690369 |
Document ID | / |
Family ID | 61687968 |
Filed Date | 2020-03-19 |
![](/patent/app/20200091451/US20200091451A1-20200319-D00000.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00001.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00002.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00003.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00004.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00005.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00006.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00007.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00008.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00009.png)
![](/patent/app/20200091451/US20200091451A1-20200319-D00010.png)
View All Diagrams
United States Patent
Application |
20200091451 |
Kind Code |
A1 |
Gotanda; Takeshi ; et
al. |
March 19, 2020 |
PHOTOELECTRIC CONVERSION ELEMENT, AND METHOD AND APPARATUS FOR
MANUFACTURING THE SAME
Abstract
A photoelectric conversion element according to an embodiment
includes: a first electrode; a second electrode; and a
photoelectric conversion layer that is in contact with the first
electrode and the second electrode and includes an active layer
containing a perovskite compound. The active layer gives an X-ray
diffraction pattern having a first diffraction peak ascribed to the
(004) plane of the perovskite compound and a second diffraction
peak ascribed to the (220) plane of the perovskite compound. The
ratio of the maximum intensity of the first diffraction peak to the
maximum intensity of the second diffraction peak is 0.18 or
more.
Inventors: |
Gotanda; Takeshi; (Yokohama,
JP) ; Jung; Hyangmi; (Yokohama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Minato-ku |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Minato-ku
JP
|
Family ID: |
61687968 |
Appl. No.: |
16/690369 |
Filed: |
November 21, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15436113 |
Feb 17, 2017 |
|
|
|
16690369 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 51/4246 20130101;
H01L 51/0029 20130101; Y02E 10/549 20130101 |
International
Class: |
H01L 51/42 20060101
H01L051/42; H01L 51/00 20060101 H01L051/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 23, 2016 |
JP |
2016-185215 |
Claims
1. A method of manufacturing a photoelectric conversion element,
the photoelectric conversion element, comprising: a first
electrode; a second electrode; and a photoelectric conversion layer
that is in contact with the first electrode and the second
electrode and includes an active layer containing a perovskite
compound, the method comprising: polishing a surface of a treatment
object containing the perovskite compound; and heat-treating the
polished treatment object.
2. The method of manufacturing the photoelectric conversion element
according to claim 1, further comprising: before the polishing,
applying a coating solution containing a precursor of the
perovskite compound to the surface of the treatment object and
forming a coating layer; and between the forming the coating layer
and the polishing, blowing a gas onto the coating layer and forming
the perovskite compound.
3. The method of manufacturing the photoelectric conversion element
according to claim 1, wherein a concentration of the precursor in
the coating solution is 1770 mg/ml or less.
4. The method of manufacturing the photoelectric conversion element
according to claim 1, further comprising before forming the coating
layer, forming an intermediate layer on the treatment object.
5. The method of manufacturing the photoelectric conversion element
according to claim 1, further comprising: between the forming the
perovskite compound and the polishing, forming a second
intermediate layer on the coating layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of and claims the benefit
of priority under 35 U.S.C. .sctn. 120 from U.S. Ser. No.
15/436,113, filed on Feb. 17, 2017, which is based upon and claims
the benefit of priority from Japanese Patent Application No.
2016-185215, filed on Sep. 23, 2016; the entire contents of which
are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a
photoelectric conversion element, and a method and an apparatus for
manufacturing a photoelectric conversion element.
BACKGROUND
[0003] A photoelectric conversion element is manufactured by using
a relatively complex method such as a vapor deposition method.
However, using a coating method or a printing method makes it
possible to simply manufacture the photoelectric conversion element
at a cost lower than ever before.
[0004] As the photoelectric conversion element, a solar cell, a
sensor, a light emitting element, and so on each using an organic
material or an organic material and an inorganic material, for
example, are under development. In developing the above-described
photoelectric conversion element, an improvement in photoelectric
conversion characteristics is required.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a top surface schematic view illustrating a
structure example of a photoelectric conversion element.
[0006] FIG. 2 is a cross-section schematic view illustrating the
structure example of the photoelectric conversion element.
[0007] FIG. 3 is a cross-section schematic view illustrating the
structure example of the photoelectric conversion element.
[0008] FIG. 4 is a view illustrating an example of an XRD
diffraction pattern.
[0009] FIG. 5 is a cross-section schematic view illustrating
another structure example of the photoelectric conversion
element.
[0010] FIG. 6 is a flowchart for explaining a manufacturing method
example of the photoelectric conversion element.
[0011] FIG. 7 is a schematic view for explaining an example of a
coating step.
[0012] FIG. 8 is a schematic view for explaining an example of a
gas supply step.
[0013] FIG. 9 is a schematic view for explaining an example of a
polishing step.
[0014] FIG. 10 is a schematic view for explaining another example
of the polishing step.
[0015] FIG. 11 is a photograph of a surface of a sample of an
example.
[0016] FIG. 12 is a photograph of a surface of a sample of an
example.
[0017] FIG. 13 is a chart illustrating IV characteristics of the
photoelectric conversion element.
[0018] FIG. 14 is a chart illustrating a conversion efficiency PCE
of the photoelectric conversion element.
[0019] FIG. 15 is a chart illustrating an open-circuit voltage
V.sub.OC of the photoelectric conversion element.
[0020] FIG. 16 is a chart illustrating an interface resistance Rs
of the photoelectric conversion element.
[0021] FIG. 17 is a chart illustrating a fill factor FF of the
photoelectric conversion element.
[0022] FIG. 18 is a chart illustrating a short-circuit current
density J.sub.SC of the photoelectric conversion element.
[0023] FIG. 19 is a chart illustrating a parallel resistance Rsh of
the photoelectric conversion element.
[0024] FIG. 20 is a chart illustrating IV characteristics of the
photoelectric conversion element.
[0025] FIG. 21 is a chart illustrating IV characteristics of the
photoelectric conversion element.
[0026] FIG. 22 is a view illustrating XRD diffraction patterns.
[0027] FIG. 23 is an enlarged view illustrating the XRD diffraction
pattern.
[0028] FIG. 24 is an enlarged view illustrating an example of the
XRD diffraction pattern.
[0029] FIG. 25 is a chart illustrating IV characteristics of the
photoelectric conversion element.
[0030] FIG. 26 is a chart illustrating IV characteristics of the
photoelectric conversion element.
[0031] FIG. 27 is a schematic chart illustrating a structure
example of the photoelectric conversion element.
[0032] FIG. 28 is a chart illustrating IV characteristics of the
photoelectric conversion element.
[0033] FIG. 29 is a chart illustrating IV characteristics of the
photoelectric conversion element.
[0034] FIG. 30 is a chart illustrating IV characteristics of the
photoelectric conversion element.
DETAILED DESCRIPTION
[0035] A photoelectric conversion element according to an
embodiment includes: a first electrode; a second electrode; and a
photoelectric conversion layer that is in contact with the first
electrode and the second electrode and includes an active layer
containing a perovskite compound. The active layer gives an X-ray
diffraction pattern having a first diffraction peak ascribed to the
(004) plane of the perovskite compound and a second diffraction
peak ascribed to the (220) plane of the perovskite compound. The
ratio of the maximum intensity of the first diffraction peak to the
maximum intensity of the second diffraction peak is 0.18 or
more.
[0036] Hereinafter, embodiments will be explained with reference to
the drawings. The drawings are schematic, and for example,
dimensions of the thickness, width, and so on of constituent
elements may differ from actual dimensions of the constituent
elements. In the embodiments, substantially the same constituent
elements are denoted by the same reference signs and an explanation
thereof will be omitted in some cases.
[0037] FIG. 1 to FIG. 3 are views illustrating a structure example
of a photoelectric conversion element. FIG. 1 is a top surface
schematic view. FIG. 2 is a cross-section schematic view taken
along the line segment X1-Y1 in FIG. 1. FIG. 3 is a cross-section
schematic view taken along the line segment X2-Y2 in FIG. 1. As the
photoelectric conversion element according to the embodiment, for
example, a light emitting element, a solar cell, a sensor, and the
like can be cited.
[0038] The photoelectric conversion element illustrated in FIG. 1
to FIG. 3 includes a substrate 1, an electrode 2, an electrode 3,
and a photoelectric conversion layer 4 in contact with the
electrode 2 and the electrode 3.
[0039] The substrate 1 supports the electrode 2, the electrode 3,
and the photoelectric conversion layer 4. The case when light
enters the photoelectric conversion layer 4 through the substrate 1
means that the substrate 1 has a light transmitting property.
[0040] The electrode 2 is provided on the substrate 1. The
electrode 2 has a function as one of an anode electrode and a
cathode electrode.
[0041] The electrode 3 is provided separately from the electrode 2
with the photoelectric conversion layer 4 interposed therebetween.
The electrode 3 is provided on the photoelectric conversion layer 4
and extends down to the substrate 1. The electrode 3 has a function
as the other of the anode electrode and the cathode electrode.
[0042] The photoelectric conversion layer 4 is provided between the
electrode 2 and the electrode 3. The photoelectric conversion layer
4 includes an active layer 41, a buffer layer 42, and a buffer
layer 43. At least one of the buffer layer 42 and the buffer layer
43 is not necessarily provided.
[0043] The active layer 41 is provided between the electrode 2 and
the electrode 3, and is provided on the buffer layer 42. In the
case of the photoelectric conversion element being a solar cell,
the active layer 41 may perform charge generation and excitation
generation by energy of the entering light. In the case of the
photoelectric conversion element being a light emitting element,
the active layer 41 may have a function as a light emitting
layer.
[0044] The active layer 41 contains a perovskite compound. The
perovskite compound is a compound having the same crystal structure
as that of perovskite.
[0045] Containing the perovskite compound enables an increase in
conversion efficiency.
[0046] The perovskite compound is expressed by a general formula:
ABX.sub.3. As A, for example, primary ammonium ions can be
utilized. Examples of the primary ammonium ion include
CH.sub.3NH.sub.3.sup.+, C.sub.2H.sub.5NH.sub.3.sup.+,
C.sub.3H.sub.7NH.sub.3.sup.+, C.sub.4H.sub.9NH.sub.3.sup.+,
HC(NH.sub.2).sub.2.sup.+, and so on. The primary ammonium ion is
preferred to be, for example, CH.sub.3NH.sub.3+, but is not limited
thereto. Further, A is also preferred to be Cs, or
1,1,1-trifluoro-ethyl ammonium iodide (FEAT), but is not limited
thereto.
[0047] As B, for example, divalent metal ions can be utilized. The
divalent metal ion is preferred to be, for example, Pb.sup.2+,
Sn.sup.2+, or the like, but is not limited thereto. When B ions are
smaller than A ions, a perovskite structure is formed easily.
[0048] As X, halogen ions can be utilized. Examples of the halogen
ion include F.sup.-, Cl.sup.-, Br.sup.-, I.sup.-, At.sup.-, and so
on. The halogen ion is preferred to be Cl.sup.-, Br.sup.-, or
I.sup.-, in particular, but is not limited thereto.
[0049] The material constituting each of A, B, and X may be a
single material or a composite material. The constituting ions can
function even though they do not necessarily match the ratio of
ABX.sub.3.
[0050] The perovskite compound has a unit lattice such as a cubic
crystal, a tetragonal crystal, or a orthorhombic crystal. An A atom
is located at each vertex, a B atom is located at the body center,
and an X atom is located at each face center of a cubic crystal
based on these locations. In this crystal structure, an octahedron
composed of one B atom and six X atoms, which is included in the
unit lattice, is easily distorted due to an interaction with the A
atoms and undergoes phase transition to a symmetric crystal. This
phase transition dramatically changes the physical property of
crystal, and electrons or holes are discharged to the outside of
the crystal to enable power generation.
[0051] When the active layer 41 is increased in thickness, a light
absorption amount increases and a short-circuit current density
J.sub.SC increases, but a carrier transportation distance
increases, and thus the loss due to deactivation tends to increase.
Therefore, for the purpose of obtaining the maximum efficiency, the
thickness of the active layer 41 is preferred to be 30 nm or more
and 1000 nm or less, and further preferred to be 60 nm or more and
600 nm or less.
[0052] As long as the thickness of the active layer 41 is adjusted
individually, the photoelectric conversion element according to the
embodiment and another general photoelectric conversion element can
be adjusted so as to have the same conversion efficiency under a
sunlight irradiation condition. However, they are different in film
properties, so that the photoelectric conversion element according
to the embodiment can achieve a conversion efficiency higher than
that of the general photoelectric conversion efficiency under a low
illuminance condition of 2001.times. or the like.
[0053] The crystal structure of the perovskite compound is analyzed
by X-ray diffraction (XRD) measurement, for example. FIG. 4 is a
view illustrating a part of an X-ray diffraction pattern of the
active layer 41 obtained by the XRD. The diffraction pattern
illustrated in FIG. 4 has a first diffraction peak ascribed to the
(004) plane of the perovskite compound within a range of 28.0 to
28.3 degrees of a diffraction angle (2.theta.) and has a second
diffraction peak ascribed to the (220) plane of the perovskite
compound near 28.5 degrees of the diffraction angle (2.theta.).
Although crystal planes are defined by Miller indices, their names
are changed by how a unit cell is defined. The first diffraction
peak sometimes overlaps with the second diffraction peak. In this
case, an inflection point in a region where a reduction in
intensity increase per unit angle is caused when seen from the
low-angle side is defined as the peak of the first diffraction
peak. Alternatively, a shape is approximated by a least square
method or the like assuming that each diffraction peak is normally
distributed at the low-angle side and the wide-angle side, and
thereby a single peak shape is found, from which the peak of the
first diffraction peak can be defined. As for the maximum intensity
ratio, as illustrated in FIG. 4, intensities a and b from a base
line are found as the maximum intensities of (004) and (220).
[0054] Having the first diffraction peak means that the crystal
structure of the perovskite compound has high stability. Further,
in the diffraction pattern illustrated in FIG. 4, the ratio of the
maximum intensity of the first diffraction peak to the maximum
intensity of the second diffraction peak is 0.18 or more. When it
is less than 0.18, the perovskite compound is not formed
sufficiently and the conversion efficiency is likely to decrease.
(004) is a crystal plane intersecting with (220) perpendicularly,
and therefore the both being detected proves that an ordered
structure of the crystal structure is formed three-dimensionally.
The case where the perovskite compound is formed using an organic
material as a base in particular does not include one to be the
origin of crystal nucleation, resulting in difficulty in crystal
growth. They being detected even in this case means that the
ordered structure is good three-dimensionally. The intensity of the
diffraction peak sometimes weakens due to not only existence of the
crystal planes, but also interference with another crystal plane,
particularly a parallel plane. In consideration of these, the ratio
of 0.18 or more means that the three-dimensional ordered structure
in the perovskite compound is enhanced.
[0055] As above, the photoelectric conversion element according to
the embodiment includes the active layer containing the perovskite
compound expressed by the above-described X-ray diffraction
pattern. The crystal structure of the above-described perovskite
compound has high stability. This makes it possible to increase the
photoelectric conversion efficiency.
[0056] The buffer layer 42 is provided between the electrode 2 and
the active layer 41 and is provided on a part of the electrode 2.
The buffer layer 43 is provided between the active layer 41 and the
electrode 3 and is provided on the active layer 41.
[0057] The buffer layer 42 and the buffer layer 43 are each
provided as one of intermediate layers. One of the buffer layer 42
and the buffer layer 43 functions as a hole transport layer, and
the other of them functions as an electron transport layer. The
hole transport layer has a function to efficiently transport holes.
The electron transport layer has a function to efficiently
transport electrons.
[0058] The substrate 1, the electrode 2, the electrode 3, the
active layer 41, the buffer layer 42, and the buffer layer 43 are
further explained.
[0059] The substrate 1 is preferably formed of a material that does
not change in quality by heat to be applied when forming electrodes
or by an organic solvent to be in contact therewith because the
electrode is formed on a surface thereof. As the material of the
substrate 1, there can be cited, for example, inorganic materials
such as non-alkali glass and quartz glass, plastics such as
polyethylene, polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), polyimide, polyamide, polyamide-imide, liquid
crystal polymer, and cycloolefin polymer, an organic material such
as a polymer film, stainless steel such as SUS, metal materials
such as aluminum, titanium, and silicon, and so on.
[0060] The light transmitting property of the substrate 1 is
appropriately selected according to the structure of the intended
photoelectric conversion element. When light enters the active
layer 41 from the substrate 1 side, a substrate having a light
transmitting property is used. When light enters the active layer
41 from the electrode 3 side, the substrate 1 does not need to have
a light transmitting property.
[0061] The thickness of the substrate 1 is not limited in
particular as long as the substrate 1 has sufficient strength for
supporting other constituent members. When the substrate 1 is
disposed on a light entrance surface side, an anti-reflection film
having, for example, a moth-eye structure can be provided on the
light entrance surface. Applying such a structure makes it possible
to efficiently take in light and improve energy conversion
efficiency of a cell. The moth-eye structure is a structure having
a regular projection array of about 100 nm on a surface thereof,
and due to this projection structure, the refractive index in a
thickness direction changes continuously. Therefore, interposition
of a non-reflective film makes the surface with a discontinuous
change in refractive index disappear, resulting in a reduction in
reflection of light and an improvement in cell efficiency. The
substrate 1 may be used alone or used in combination to exhibit the
function of the photoelectric conversion element. Specifically, a
solar cell having had the present application applied thereto may
be formed on an already-completed silicon solar cell to fabricate a
tandem solar cell. In this case, an equivalent circuit is preferred
to be a parallel circuit. Further, the first electrode and the
intermediate layer may be shared with the silicon solar cell. In
this case, the equivalent circuit is preferred to be a series
circuit.
[0062] A material having conductivity can be used for the electrode
2 and the electrode 3. A material having a light transmitting
property and conductivity may be used for the electrode 2 and the
electrode 3. Examples of the material applicable to the electrode 2
and the electrode 3 include metal oxide materials such as an indium
oxide, a zinc oxide, a tin oxide, an indium tin oxide (ITO) being a
composite body of these, a fluorine-doped tin oxide (FTO), and a
film (NESA or the like) fabricated by using electrically conductive
glass made of indium, zinc, oxide, and the like, and metal
materials such as gold, platinum, silver, and copper. Particularly,
ITO or FTO is preferred. At least one of the electrode 2 and the
electrode 3 may have a single-layer structure or a stacked-layer
structure of layers containing materials with different work
functions.
[0063] The thickness of at least one of the electrode 2 and the
electrode 3 is preferred to be 30 nm or more and 300 nm or less in
the case of the material of the electrode being ITO. When it is
less than 30 nm, conductivity is likely to decrease to increase
resistance. When the resistance is large, the photoelectric
conversion efficiency decreases in some cases. When it becomes
greater than 300 nm, flexibility of an ITO film decreases and
cracking sometimes occurs when stress is applied. At least one of
the electrode 2 and the electrode 3 preferably has a sheet
resistance of 10.OMEGA./ or less.
[0064] When the electrode 2 or the electrode 3 is brought into
contact with the electron transport layer, a material having a low
work function is preferably used as the electrode material.
Examples of the material with a low work function include alkali
metal, alkali-earth metal, and so on. Concrete examples include Li,
In, Al, Ca, Mg, Sm, Tb, Yb, Zr, Na, K, Rb, Cs, Ba, and alloys of
the above. Further, the material may be an alloy of the metal
selected from the above-described materials low in work function
and a metal with a relatively high work function selected from
gold, silver, platinum, copper, manganese, titanium, cobalt,
nickel, tungsten, tin, and so on. Examples of the alloy usable for
the electrode material include a lithium-aluminum alloy, a
lithium-magnesium alloy, a lithium-indium alloy, a magnesium-silver
alloy, a calcium-indium ally, a magnesium-aluminum alloy, an
indium-silver alloy, a calcium-aluminum alloy, and so on.
[0065] In the case of using the above-described material, the
thickness of the electrode is preferred to be 1 nm or more and 500
nm or less, and more preferred to be 10 nm or more and 300 nm or
less. When it is 1 nm, it is difficult to sufficiently transmit
generated charges to an external circuit because the resistance is
too large. When it becomes greater than 500 nm, a long period of
time is required for electrode formation, to thus increase a
material temperature and damage the other materials, resulting in
deterioration of performance in some cases. Further, a large amount
of material is used, to thus prolong the time of occupying a
deposition apparatus, resulting in an increase in cost in some
cases.
[0066] An organic material can also be used as the electrode
material. A conductive high-molecular compound such as, for
example, polyethylenedioxythiophene (PEDOT) or the like is
preferred. Such a conductive high-molecular compound is put on the
market, and there can be cited, for example, Clevios P H 500,
Clevios P H, Clevios P VP Al 4083, Clevios HIL 1, 1 (product name,
manufactured by H.C. Starck), and so on. The work function (or
ionization potential) of PEDOT is 4.4 eV, but the work function of
the electrode can be adjusted by combining another material with
PEDOT. For example, mixing polystyrenesulfonate (PSS) in PEDOT
makes it possible to adjust the work function in a range of 5.0 to
5.8 eV. However, a layer formed of a combination of the conductive
high-molecular compound and another material has a possibility that
its carrier transportability deteriorates because the ratio of the
conductive high-molecular compound decreases relatively. Therefore,
the thickness of the electrode in such a case is preferred to be 50
nm or less, and more preferred to be 15 nm or less. As the
conductive high-molecular compound, polypyrrole, polythiophene, and
polyaniline are preferred.
[0067] When one of the buffer layer 42 and the buffer layer 43
functions as the electron transport layer, the electron transport
layer preferably contains a halide or a metal oxide. Preferred
examples of the halide include LiF, LiCl, LiBr, LiI, NaF, NaCl,
NaBr, NaI, KF, KCl, KBr, KI, and CsF. LiF is particularly preferred
among the above. Preferred examples of the metal oxide include a
titanium oxide, a molybdenum oxide, a vanadium oxide, a zinc oxide,
a nickel oxide, a lithium oxide, a calcium oxide, a cesium oxide,
an aluminum oxide, and a niobium oxide. The titanium oxide is
preferred among the above. As the titanium oxide, an amorphous
titanium oxide that can be obtained by hydrolyzing titanium
alkoxide by a sol-gel method is preferred.
[0068] The electron transport layer may contain an inorganic
material such as metal calcium. The thickness of the electron
transport layer is preferred to be 20 nm or less. This makes it
possible to lower film resistance of the electron transport layer
to increase the conversion efficiency. The thickness of the
electron transport layer is preferred to be 5 nm or more. This
makes it possible to sufficiently exhibit a hole-blocking effect
and prevent generated excitations from being deactivated before
electrons and holes are discharged. Consequently, it is possible to
efficiently take out current.
[0069] An n-type organic semiconductor is preferred to be fullerene
and a derivative thereof, but is not limited thereto in particular.
Examples thereof include derivatives whose basic frameworks are
C60, C70, C76, C78, C84, and the like. The fullerene derivative may
be one whose carbon atoms in the fullerene framework are modified
by arbitrary functional groups, and these functional groups may be
bonded each other to form a ring. The fullerene derivative includes
a fullerene-bonded polymer. The fullerene derivative that has a
functional group high in affinity to a solvent and has high
solubility to the solvent is preferred.
[0070] Examples of the functional group in the fullerene derivative
include: a hydrogen atom; a hydroxyl group; a halogen atom such as
a fluorine atom and a chlorine atom; an alkyl group such as a
methyl group and an ethyl group; an alkenyl group such as a vinyl
group; a cyano group; an alkoxy group such as a methoxy group and
an ethoxy group; an aromatic hydrocarbon group such as a phenyl
group and a naphthyl group; an aromatic heterocyclic group such as
a thienyl group and a pyridyl group; and so on. Specific examples
of the fullerene derivative include fullerene hydride such as
C.sub.60H.sub.36 and C.sub.70H.sub.36, oxidized fullerene such as
C.sub.60 and C.sub.70, a fullerene metal complex, and so on. As the
fullerene derivative,
[0071] PCBM([6,6]-phenylC.sub.61butyric acid methylester) or
[0072] PCBM([6,6]-phenylC.sub.71butyric acid methylester) is
particularly preferably used.
[0073] When the other of the buffer layer 42 and the buffer layer
43 functions as the hole transport layer, the hole transport layer
can contain a p-type organic semiconductor material and an n-type
organic semiconductor material. The p-type organic semiconductor
material and the n-type organic semiconductor material mentioned
here indicate materials that can function as an electron donor
material and an electron acceptor material when heterojunction and
bulk heterojunction are formed.
[0074] As the n-type organic semiconductor, a low-molecular
compound capable of forming a film by vapor deposition can be used.
The low-molecular compound mentioned here indicates a compound
whose number average molecular weight Mn and weight average
molecular weight Mw agree. Either of them is 10000 or less.
BCP(bathocuproine), Bphen(4,7-diphenyl-1,10-phenanthroline),
TpPyPB(1,3,5-tri(p-pyrid-3-yl-phenyl)benzene), and DPPS(diphenyl
bis(4-pyridin-3-yl)phenyl)silane) are more preferred.
[0075] A p-type organic semiconductor preferably contains a
copolymer composed of a donor unit and an acceptor unit, for
example. As the donor unit, fluorene, thiophene, or the like can be
used. As the acceptor unit, benzothiadiazole or the like can be
used. Specifically, it is possible to use polythiophene and its
derivative, polypyrrole and its derivative, a pyrazoline
derivative, an arylamine derivative, a stilbene derivative, a
triphenyldiamine derivative, oligothiophene and its derivative,
polyvinyl carbazole and its derivative, polysilane and its
derivative, a polysiloxane derivative having aromatic amine at a
side chain or a main chain, polyaniline and its derivative, a
phthalocyanine derivative, porphyrin and its derivative,
polyphenylene vinylene and its derivative, polythienylene vinylene
and its derivative, a benzodithiophene derivative, a
thieno[3,2-b]thiophene derivative, or the like. For the hole
transport layer, these materials may be used in combination, or a
copolymer composed of comonomers constituting these materials may
be used. Among the above, polythiophene and its derivative have
excellent stereoregularity and are relatively high in solubility to
a solvent, and thus are preferred.
[0076] As the material of the hole transport layer, a derivative
such as
poly[N-9'-heptadecanyl-2,7-carbazole-alto-5,5-(4',7'-di-2-thienyl-2',1',3-
'-benzothiadiazole)] (PCDTBT) being a copolymer containing
carbazole, benzothiadiazole and thiophene may be used. Further, a
copolymer of a benzodithiophene (BDT) derivative and a
thieno[3,2-b]thiophene derivative is also preferred. For example,
poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][-
3-fluoro-2-[(2-ethylhexyl)carbonyl)]thieno[3,4-b]thiophenediyl]]
(PTB7), PTB7-Th into which a thienyl group having an electron
donating property weaker than that of an alkoxy group of PTB7 is
introduced (PCE10, or PBDTTT-EFT), and so on are also preferred.
Further, as the material of the hole transport layer, a metal oxide
can also be used. Preferred examples of the metal oxide include a
titanium oxide, a molybdenum oxide, a vanadium oxide, a zinc oxide,
a nickel oxide, a lithium oxide, a calcium oxide, a cesium oxide,
and an aluminum oxide. These materials have an advantage of being
inexpensive. Further, as the material of the hole transport layer,
thiocyanate such as copper thiocyanate may be used.
[0077] For a transport material such as Spiro-OMeTAD and the p-type
organic semiconductor, a dopant can be used. As the dopant, it is
possible to use oxygen, 4-tert-butylpyridine,
lithium-bis(trifluoromethanesulfonyl)imide(Li-TFSI), acetonitrile,
tris[2-(1H-pyrazole-1-yl)pyridine]cobalt(III)tris(hexafluorophosphate),
tris[2-(1H-pyrazole-1-yl)pyrimidine]cobalt(III)tris[bis(trisfluoromethyls-
ulfonyl)imide](MY11), or the like.
[0078] As the hole transport layer, a conductive high-molecular
compound such as polyethylenedioxythiophene can be utilized. For
such a conductive high-molecular compound, a material applicable to
the electrodes 2 and 3 can be used. In the hole transport layer as
well, the material can be adjusted to a material having a work
function appropriate as the hole transport layer or the like by
combining another material with a polythiophene-based polymer such
as PEDOT. Here, the work function of the hole transport layer is
preferably adjusted to be lower than a valence band of the active
layer 41. Further, it can be adjusted by mixing PSS with PEDOT.
[0079] The structure example of the photoelectric conversion layer
4 is not limited to the structure illustrated in FIG. 1 to FIG. 3.
FIG. 5 is a cross-section schematic view illustrating another
structure example of the photoelectric conversion element.
[0080] The photoelectric conversion element illustrated in FIG. 5
includes a photoelectric conversion layer 4 further including a
base layer 44 and a protective layer 45 in addition to the
configuration illustrated in FIG. 1 to FIG. 3.
[0081] The base layer 44 is provided between the electrode 2 and
the active layer 41 as one of the intermediate layers. The base
layer 44 is preferably made of a low-molecular compound. The
low-molecular compound mentioned here means that the number average
molecular weight Mn and the weight average molecular weight Mw
agree and they are 10000 or less each. As the low-molecular
compound, there can be cited, for example, materials containing
low-molecular compounds such as organosulfur molecules, organic
selenium/tellurium molecules, a nitrite compound, monoalkylsilane,
carboxylic acid, phosphonic acid, phosphoric ester, organic silane
molecules, unsaturated hydrocarbon, alcohol, aldehyde, alkyl
bromide, a diazo compound, and alkyl iodide. For example,
4-fluorobenzoic acid (FBA) is preferred. Further, as the base layer
44, an organic material applicable to the electrode 2 may be used.
In this case, the base layer 44 may be regarded as a part of the
electrode 2.
[0082] The base layer 44 is formed by applying a solution
containing the low-molecular compound on the electrode 2 and drying
the solution. The base layer 44 can improve collection efficiency
of carries moving from the active layer 41 to the electrode 2 or
the electrode 3 by means of vacuum level shift caused a dipole. The
base layer 44 enables an improvement in crystallinity of the
perovskite compound, suppression of pin holes to occur in the
active layer 41, and an increase in amount of transmitted light on
the light-receiving surface side. This makes it possible to
increase a current density, improve the fill factor FF, and improve
the photoelectric conversion efficiency and light emission
efficiency.
[0083] The base layer 44 is provided when forming the active layer
41 containing the perovskite compound on a large lattice-mismatched
crystal-based buffer layer other than a titanium oxide and an
aluminum oxide in particular or an electrode, and thereby the base
layer 44 itself can be a stress relaxation layer, or a stress
relaxation function can be given to a part of the perovskite
compound adjacent to the base layer 44. The base layer 44 enables
release of internal stress caused by crystal growth, suppression of
generation of pin holes in the active layer 41, and achievement of
good interface junction as well as an improvement in crystallinity
of the perovskite compound.
[0084] As the base layer 44, a base layer made of a metal oxide
having a mesoporous structure or a dense structure with no voids
and the like can be used. As a metal element, titanium, silicon,
copper, molybdenum, nickel, zinc, niobium, tin, vanadium, or
tungsten is more preferred. Providing the base layer 44 enables
suppression of a leakage current between the electrode 2 and the
electrode 3 even though pin holes, cracks, voids, or the like occur
in the active layer 41.
[0085] When the crystallinity of the perovskite compound increases,
separation occurs between the base layer 44 and the perovskite
compound, resulting in that a decrease in conversion efficiency is
caused in some cases. This is caused because the internal stress
caused by crystal growth is accumulated. In order to absorb this, a
soft organic material is preferably used to form the base layer 44.
When rearrangement of ions is performed by a heat treatment in
particular, a further increase in internal stress due to a thermal
expansion coefficient difference occurs, and thus the organic
material is required as stress relaxation.
[0086] The protective layer 45 is provided between the electrode 3
and the active layer 41 as one of the intermediate layers. The
protective layer 45 only needs to have a structure enabling
exposure of a projection of an up and down structure formed on the
surface of the active layer 41 in a polishing step. As a material
applicable to the protective layer 45, there can be cited, for
example, a halide, an inorganic oxide, an organic low-molecular
material, a high-molecular material, and so on. When the protective
layer 45 has carrier transportability, the protective layer 45 can
be made to function as a buffer layer. In this case, a material
applicable to the buffer layer 42 or the buffer layer 43 may be
used for the protective layer 45.
[0087] Further, what is called a back contact system structure in
which the electrode 2 and/or the buffer layer 42 and the electrode
3 and/or the buffer layer 43 are disposed separately from each
other in one direction of the active layer 41 may be included.
[0088] Next, there will be explained a manufacturing method example
of the photoelectric conversion element according to the
embodiment. FIG. 6 is a flowchart for explaining the manufacturing
method example of the photoelectric conversion element according to
the embodiment. The manufacturing method example of the
photoelectric conversion element according to the embodiment
includes a first electrode forming step S1, a photoelectric
conversion layer forming step S2, a second electrode forming step
S3, and a heat treatment step S4. The method of manufacturing the
photoelectric conversion element according to the embodiment is not
limited to the above-described manufacturing method example.
[0089] In the first electrode forming step S1, the electrode 2 is
formed on the substrate 1 by using, for example, a vacuum
deposition method, a sputtering method, an ion plating method, a
plating method, a coating method, or the like.
[0090] In the photoelectric conversion layer forming step S2, the
photoelectric conversion layer 4 is formed on the electrode 2. The
photoelectric conversion layer forming step S2 includes a first
buffer layer (base layer) forming step S2-1, a coating step S2-2, a
gas blowing step S2-3, a protective layer forming step S2-4, a
polishing step S2-5, and a second buffer layer forming step
S2-6.
[0091] In the first buffer layer (base layer) forming step S2-1, at
least one of the buffer layer 42 and the base layer 44 as the
intermediate layer is formed on the electrode 2 by using, for
example, a vacuum deposition method, a sputtering method, an ion
plating method, a plating method, a coating method, or the like.
The base layer 44 is preferably formed by using, for example, a
coating method. When the buffer layer 42 and the base layer 44 are
not formed, the first buffer layer (base layer) forming step S2-1
is not performed.
[0092] FIG. 7 is a schematic view for explaining the coating step
S2-2. In the coating step S2-2, with use of a coating method, a
coating solution 63a is applied onto an intermediate layer of a
treatment object 62 disposed on a support 61 from a coater 63 to
then form a coating layer 62a. The coating layer 62a may be formed
using a coating apparatus including the coater 63. Supply of the
coating solution 63a by the coater 63 is controlled by a controller
provided separately.
[0093] The support 61 includes a rotation shaft 61a and a support
surface 61b supporting the treatment object 62. The rotation shaft
61a is vertical to the support surface 61b. The support 61 fixes
the treatment object 62 on the support surface 61b using a vacuum
chuck. When forming the coating layer 62a, the support 61 rotates
about the rotation shaft 61a.
[0094] The coating solution 63a contains a precursor of the
perovskite compound and an organic solvent capable of dissolving
the precursor. Examples of the organic solvent include
N,N-dimethylformamide (DMF), .gamma.-butyrolactone,
dimethylsulfoxide (DMSO), and so on. A mixed solvent of a plurality
of materials may be used as the organic solvent. The coating
solution may contain a single solvent and a plurality of raw
materials for forming the perovskite compound that are dissolved in
the solvent.
[0095] A concentration of the precursor in the coating solution 63a
is preferred to be 1770 mg/ml or less. When it becomes greater than
1770 mg/ml, a crystal grain diameter of the perovskite compound
increases, to make pin holes or the like occur easily in the active
layer 41 in the polishing step S2-5.
[0096] The coating layer 62a may be formed in a manner that, for
example, a plurality of solutions individually containing a
plurality of raw materials for forming the perovskite compound are
prepared to be sequentially applied using a spincoater, a slit
coater, a bar coater, a dip coater, or the like.
[0097] The coating solution 63a may further contain an additive. As
the additive, for example, 1,8-diiodooctane (DIO), or
N-cyclohexyl-2-pyrrolidone (CHP) is preferably used.
[0098] When the active layer 41 has a mesoporous structure
generally, a leakage current between the electrodes can be
suppressed even when pin holes, cracks, voids, or the like occur in
the active layer 41. When the active layer 41 does not have a
mesoporous structure, such an effect cannot be obtained easily.
However, in this embodiment, when the plural raw materials are
contained in the coating solution 63a as the precursor of the
perovskite compound, less volume shrinkage occurs at the time of
forming the active layer 41, thus making it possible to reduce pin
holes, cracks, and voids.
[0099] By application of a solution containing methylammonium
iodide (MAI), a metal halide, and the like after application of the
coating solution 63a, reaction with the unreacted metal halide
progresses, resulting in that a film with fewer pin holes, cracks
and voids is obtained easily. Thus, a solution containing, for
example, MAI is preferably applied on the surface of the coating
layer 62a after application of the coating solution 63a. The MAI
solution is preferably applied after the gas blowing step S2-3.
[0100] FIG. 8 is a schematic view for explaining the gas blowing
step S2-3. In the gas blowing step S2-3, a gas 71a is blown onto
the coating layer 62a from a gas supply 71 to then form the
perovskite compound. The gas 71a may be blown onto the coating
layer 62a using a coating apparatus including the gas supply 71.
Supply of the gas 71a by the gas supply 71 is controlled by the
controller provided separately.
[0101] As the gas 71a, for example, nitrogen, or helium, neon, or
argon, which is classified as a rare gas, is preferably used.
Further, as the gas 71a, air, oxygen, carbon dioxide, or the like
can also be used. These gases can be used independently, or used by
mixture. The nitrogen gas is preferred because it is inexpensive
and can be used by separating from the atmosphere.
[0102] A concentration of moisture in the gas 71a is 50% or less,
and preferred to be 4% or less. The lower limit value of the
concentration of moisture in the gas 71a is preferred to be 10 ppm
or more.
[0103] The gas 71a may contain vapor of a substance that is liquid
at room temperature. As the substance liquid at room temperature,
for example, N,N-dimethylformamide (DMF), .gamma.-butyrolactone,
dimethylsulfoxide (DMSO), chlorobenzene (CB), dichlorobenzene
(DCB), or the like can be used. The vapor of the substance liquid
at room temperature can improve smoothness of the active layer 41
and improve stability of the perovskite compound.
[0104] A temperature of the gas 71a is preferred to be 30.degree.
C. or less. When it becomes greater than 30.degree. C., solubility
of the precursor of the perovskite compound contained in the
coating solution 63a increases to then hinder formation of the
perovskite compound. In the meantime, a temperature of the
treatment object 62 (substrate temperature) is preferably lower
than that of the gas. The temperature of the treatment object 62 is
preferred to be, for example, 20.degree. C. or less, and further
preferred to be 15.degree. C. or less.
[0105] Blowing the gas 71a removes the organic solvent during a
process of the perovskite compound being formed, and enables
acceleration of the forming reaction of the perovskite compound.
Blowing the gas 71a accelerates the forming reaction of the
perovskite compound even without application of heat, and thus it
is possible to suppress formation of pin holes, cracks, or voids in
the active layer 41. Further, with no application of heat, rapid
drying of the surface of the coating layer 62a is suppressed, to
enable suppression of a stress difference between the coating
surface and the inside. Therefore, the surface smoothness of the
active layer 41 to be formed increases, to enable an improvement in
the fill factor FF and an improvement in operating life.
[0106] The gas blowing needs to be performed before the forming
reaction of the perovskite compound is completed in the coating
solution 63a. That is, it is necessary to accelerate the reaction
by the gas blowing. The gas blowing is preferably started
immediately after the coating layer 62a is formed. Specifically, it
is preferably started within 10 seconds, and more preferably
started within one second after the coating is completed.
[0107] During a process of the coating layer 62a drying, single
crystals of MAI, lead iodide, and the like, which are the raw
materials, also grow simultaneously with the formation of the
perovskite compound in some cases. As the raw materials are allowed
to dry more quickly from the state where they are dissolved and
dispersed in the coating layer 62a, the perovskite compound is
allowed to grow more efficiently. Accordingly, the manufacturing
method example of the photoelectric conversion element according to
the embodiment is effective when the perovskite compound is formed
on an organic film or an oxide having a large lattice mismatch.
[0108] When the ratio of the conductive high-molecular compound to
be used for the electrode or the like decreases relatively, the
coating solution 63a containing the precursor of the perovskite
compound is likely to be repelled due to the effect of surface
energy. This facilitates occurrence of pin holes in the active
layer 41. In such a case, by blowing a nitrogen gas or the like,
drying of the solvent is preferably completed before the coating
solution 63a is repelled.
[0109] Progress of the reaction can be observed by measuring an
absorption spectrum of the coating layer 62a. That is, with the
perovskite compound being formed, light transmittance of the
coating layer 62a decreases. Therefore, visual observation reveals
that the coating is changing in color to brown as the reaction
progresses. For the purpose of quantitatively observing such a
color change, the absorption spectrum of the coating is measured.
When such an observation is performed, it is preferred to measure
an absorption spectrum of a wavelength that is unlikely to be
affected by absorptions of the raw materials contained in the
coating solution 63a and facilitates observation of absorption by
the perovskite compound. Specifically, the absorption spectrum of a
wavelength in a region of 700 to 800 nm is preferably measured. No
absorption spectrum measurement is required to be performed in this
entire region, and thus an absorption spectrum of a specific
wavelength, for example, 800 nm, only needs to be observed. The
absorption spectrum is measured by using, for example, visible and
ultraviolet spectroscopy (UV-VIS) or the like, but the method is
not limited in particular. As a light source, a deuterium discharge
tube, a tungsten lump, or a xenon lump can be used, and a
spectroscope, a detector, and the like are combined to perform the
measurement.
[0110] The absorption spectrum can be measured with a transmitted
light at the coating stage of the coating solution 63a when the
substrate 1, the electrode 2, and the like are transparent. In the
meantime, in the case of no sufficient transparency, a reflected
light on the coating surface is observed, thereby enabling the
measurement.
[0111] When the coating solution 63a containing the precursor of
the perovskite compound is in contact with a layer containing the
organic material, which is, for example, the electrode 2, the
buffer layer 42, or the base layer 44, a period of time for the gas
blowing is preferred to be 45 seconds or more, and more preferred
to be 120 seconds or more.
[0112] A flow rate of the gas 71a is preferred to be, for example,
3 L/minute or more and 20 L/minute or less. As the flow rate of the
gas flowing on the coating surface is larger, the progress of the
forming reaction of the perovskite compound is accelerated.
Further, the flow rate of the gas is preferred to be small in order
to prevent fluctuations of the coating surface due to the gas
flow.
[0113] The gas supply 71 blows the gas through a nozzle having a
gas blowing port, and a leading end of the nozzle is preferably
directed to the coating surface, and further the leading end of the
nozzle is preferably close to the surface of the coating layer
62a.
[0114] After the gas blowing, the coating solution containing the
precursor of the perovskite compound may be applied a plurality of
times. The coating solution is applied using, for example, a
spincoater, a slit coater, a bar coater, a dip coater, or the like.
A coating layer formed by the first application tends to be a
lattice mismatched layer, and thus the coating solution is
preferably applied so as to have a relatively thin thickness.
Specifically, such conditions as to reduce the film thickness are
preferred in which a rotation speed of the spincoater is relatively
fast, a slit width of the slit coater and the bar coater is
relatively narrow, a pulling-up speed of the dip coater is
relatively fast, a solute concentration in the coating solution is
relatively weak, and the like.
[0115] In a two-step method or a conventional method called a
sequential deposition method or the like, the gas blowing is
sometimes performed after the forming reaction of the perovskite
compound is completed, namely after sufficient color development
occurs due to the reaction. However, this is just performed for
drying the solvent component. The gas blowing is effective in the
photoelectric conversion element that includes the base layer 44
having a mesoporous structure and made of titanium oxide, aluminum
oxide, or the like because the gas blowing facilitates
crystallization of the perovskite compound. However, the gas
blowing is less effective for the forming reaction of the
perovskite compound on the organic film and the oxide having a
large lattice mismatch other than the above. When the perovskite
compound is formed on the organic film or the oxide having a large
lattice mismatch, as described in the embodiment, before the
forming reaction of the perovskite compound is completed, the gas
is blown to accelerate the forming reaction of the perovskite
compound. Thereby, it is possible to achieve suppression of a
defect structure such as pin holes, cracks, or voids. The gas
blowing performed when applying a certain material before forming a
perovskite structure is very effective for the subsequent forming
reaction of the perovskite structure on the organic film or the
oxide having a large lattice mismatch.
[0116] After the gas blowing, a heat treatment is preferably
performed in order to dry the solvent (a heat treatment step
S2-3-2). The heat treatment is performed by a heater. The heat
treatment is performed for removing the organic solvent contained
in the coating layer 62a, to thus be performed preferably before
the buffer layer 43 and the like are formed. A heat treatment
temperature is preferred to be 50.degree. C. or more, and further
preferred to be 90.degree. C. or more, and its upper limit is
preferred to be 200.degree. C. or less, and further preferred to be
150.degree. C. or less. The heat treatment is performed at such a
temperature. The case when the heat treatment temperature is low
has a problem of being incapable of removing the solvent
sufficiently, and the case when the heat treatment temperature is
too high has a problem that the surface of the active layer 41
becomes rough to make it impossible to obtain a smooth surface.
[0117] In the protective layer forming step S2-4, the protective
layer 45 as one of the intermediate layers is formed on the coating
layer 62a using, for example, a vacuum deposition method, a
sputtering method, an ion plating method, a plating method, a
coating method, or the like. At this time, a bulge (projection) of
the coating layer 62a may penetrate the protective layer 45 to be
exposed.
[0118] FIG. 9 is a schematic view for explaining the polishing step
S2-5. In the polishing step S2-5, the surface of the treatment
object 62 is polished using a polishing roller 81. The polishing
roller 81 is movable by a mover 82. The mover 82 is controlled by a
controller 83. The polishing is performed for smoothing the surface
of the treatment object 62. Such polishing as to expose only the
projection on the surface of the coating layer 62a is preferably
performed after the protective layer 45 is formed in
particular.
[0119] An abrasive is used for the polishing by the polishing
roller 81. As the abrasive, there can be used, for example, brown
fused alumina abrasives, white fused alumina abrasives, rudy fused
alumina abrasives, mono-crystalline fused alumina abrasives,
artificial emery abrasives, fused alumina zirconia abrasives, black
silicon carbide abrasives, green silicon carbide abrasives, or the
like, which are described in JIS R6111. As the grain size of fine
powder for polishing, there can be used #240, #280, #320, #360,
#400, #500, #600, #700, #800, #1000, #1200, #1500, #2000, #2500,
#3000 or the like, which is described in JIS R6001. Further, a
nonwoven fabric, a sponge of polyvinyl alcohol, or the like can be
used.
[0120] The polishing roller 81 includes a rotation shaft 81a and a
polishing surface 81b for polishing the surface of the treatment
object 62 by rotating about the rotation shaft 81a. At the time of
polishing, the mover 82 moves at least one of the polishing roller
81 and the treatment object 62 so that the surface of the treatment
object 62 comes into contact with the polishing surface 81b of the
polishing roller 81 parallel to the rotation shaft 81a. This makes
it difficult for flaws to be caused in the treatment object 62, or
for wastes from the polishing to remain. FIG. 9 illustrates an
example where the mover 82 moves the polishing roller 81. The
polishing roller 81 may be moved along one direction parallel to
the support surface 61b while rotating.
[0121] The treatment object 62 may be polished while being moved by
a roll-to-roll process. FIG. 10 is a schematic view for explaining
another example of the polishing step S2-5. In the case of a
configuration illustrated in FIG. 10, the position of the polishing
roller 81 may be fixed. In this case, the mover 82 does not need to
be provided.
[0122] A support 91 illustrated in FIG. 10 includes a rotation
shaft 91a parallel to the rotation shaft 81a and a support surface
91b supporting the treatment object 62 while rotating about the
rotation shaft 91a. A support 92 includes a rotation shaft 92a
parallel to the rotation shaft 81a and a support surface 92b
supporting the treatment object 62 while rotating about the
rotation shaft 92a. A support 93 includes a rotation shaft 93a
parallel to the rotation shaft 81a and a support surface 93b
supporting the treatment object 62 while rotating about the
rotation shaft 93a. The positions of the supports 91 to 93 may be
fixed.
[0123] The support 91 rotates in the same rotation direction as
that of the support 92, and rotates in a rotation direction reverse
to that of the polishing roller 81 and the support 93. The supports
92 and 93 are controlled by a controller 94. The support 91 is
controlled by a controller provided separately or the controller
94. The treatment object 62 is transferred along one direction by
the support 91 to the support 93.
[0124] The controllers such as the controller 83 and the controller
94 are configured by using hardware using a processor and the like,
for example. Each operation may be stored as an operating program
in a computer-readable recording medium such as a memory, and each
operation may be executed by the hardware reading the operating
program stored in the recording medium as required.
[0125] The rotation shafts 91a to 93a extend in a direction
parallel to the rotation shaft 81a. The supports 91 to 93 are each
controlled by the controller 94 so as to rotate at a rotation speed
slower than that of the polishing roller 81, thereby enabling
polishing while the treatment object 62 moving. Wastes generated by
the polishing are removed by a cleaning device 95. The cleaning
device 95 using a gas blow is preferred.
[0126] In the second buffer layer forming step S2-6, the buffer
layer 43 is formed on the protective layer 45 by using, for
example, a vacuum deposition method, a sputtering method, an ion
plating method, a plating method, a coating method, or the like.
When the buffer layer 43 is not provided, the second buffer layer
forming step S2-6 is not performed.
[0127] In the second electrode forming step S3, the electrode 3 is
formed on the photoelectric conversion layer 4 by using, for
example, a vacuum deposition method, a sputtering method, an ion
plating method, a plating method, a coating method, or the
like.
[0128] In the heat treatment step S4, in order to heat the
treatment object 62, for example, the heater performs the heat
treatment on a stack including the substrate 1, the electrode 2,
the electrode 3, and the photoelectric conversion layer 4. In this
manner, a semiconductor element can be manufactured.
[0129] The heat treatment enables rearrangement of ions in the
perovskite compound having strain formed by the polishing. The ions
in the perovskite compound may be rearranged by voltage application
in place of the heat treatment. A heat treatment temperature is
preferred to be 50.degree. C. or more, and further preferred to be
90.degree. C. or more, for example. The heat treatment temperature
is preferred to be 200.degree. C. or less, and further preferred to
be 150.degree. C. or less. The case when it is less than 50.degree.
C. requires time for rearrangement. The case when it becomes
greater than 200.degree. C. has a problem that the surface of the
coating layer 62a becomes rough and does not obtain smoothness. In
the case of no rearrangement, the conversion efficiency becomes
lower than before the polishing. This is because carrier transfer
efficiency is poor and FF and J.sub.SC decrease. The method of
manufacturing the photoelectric conversion element according to
this embodiment is suitable also for the case of manufacturing a
planar photoelectric conversion element with no base layer 44.
[0130] The respective steps of the above-described manufacturing
method example are performed using, for example, an apparatus for
manufacturing the photoelectric conversion element. The apparatus
for manufacturing a semiconductor element includes the support 61
and the coater 63 that are illustrated in FIG. 7, the gas supply 71
illustrated in FIG. 8, and the polishing roller 81, the mover 82,
and the controller 83 that are illustrated in FIG. 9, for example.
Further, the manufacturing apparatus may include the configuration
illustrated in FIG. 10. The apparatus for manufacturing the
semiconductor element may further include a mechanism for forming
the electrodes 2 and 3, a mechanism for forming each of the buffer
layers 42 and 43, the base layer 44, and the protective layer 45,
and a heater that heats the stack including the electrodes 2 and 3
and the photoelectric conversion layer 4.
EXAMPLE
[0131] The photoelectric conversion element utilizing the
perovskite compound has been evaluated using a small element with a
power generation area of about 2 mm square. The element utilizing
the perovskite compound is fabricated by deposition accompanied by
crystal growth and has internal stress generated therein due to
volume shrinkage, and thus has a problem of occurrence of pin holes
and causing interlayer peeling and the like. Thus, it was difficult
to fabricate a layer structure with few structure defects. For this
reason, in places of mass production, conversion efficiency
reproducibility was low and variations were large. For this reason,
there was sometimes a case that a high conversion efficiency was
able to be obtained unusually in some products having few defects
accidentally, but it was difficult to obtain a high conversion
efficiency uniformly on a broad basis.
[0132] In the meantime, it is necessary to manufacture an element
allowing achievement of high efficiency on a broader basis for
practical application. Therefore, in the following examples,
elements each having a power generation area of 1 cm square were
manufactured, and their comparison and examination were performed.
A solar cell fabricated by coating is normally fabricated in which
strip-shaped cells each having a width of about 1 cm are configured
in series. Therefore, the element with a 1-cm square power
generation area has an appropriate size to be an index of actual
module performance.
Example 1
[0133] An ITO film as a first electrode was formed on a glass
substrate. A base layer containing PEDOT was formed on the ITO
film. The base layer functions also as the hole transport layer.
The PEDOT being PSS was dried at 140.degree. C. for 10 minutes
after HIL 1.1 was spin-coated at 5000 rpm. Then, a coating layer
containing a precursor of perovskite made of methylammonium iodide
and lead iodide was formed. A coating solution containing a
precursor of a perovskite compound was prepared by dissolving
methylammonium iodide and lead iodide in DMF. At this time, the
methylammonium iodide was adjusted to be 200 mg/ml, and the lead
iodide was adjusted to be 578 mg/ml. This solution was spin-coated
onto the base layer at 500 rpm.
[0134] After the coating, gas blowing was started before a change
in color, and then the blowing was stopped after confirmation of
appearance of a change in color. A nitrogen gas was used for the
gas, and was blown through a nozzle having a 6-mm inside diameter
at 5 L/minute (40 km/l). The nozzle was disposed so that the center
of the nozzle was located on the normal of a center portion of the
glass substrate, and a distance from the nozzle to the substrate
was set to 0.5 cm. The blowing was performed for 120 seconds.
[0135] A solution was prepared in which PCBM was dissolved in DCB
so as to have a PCBM concentration of 20 mg/ml, and was spin-coated
onto an active layer fabricated using the coating layer at 400 rpm
for 120 s. During this period, nitrogen was introduced into a
spincoater to accelerate drying. Then, the surface was polished
using a Bellclean E-1 (manufactured by AION Co., Ltd.). After
completion of the polishing, the PCBM was spin-coated again under
the same condition to fabricate a sample. Further, a sample
obtained after the PCBM was spin-coated under the same condition
without polishing was fabricated separately.
[0136] FIG. 11 is a photograph of the sample with no polishing, and
FIG. 12 is a photograph of the sample on which polishing was
performed. The sample shown in FIG. 11 has spots on its surface.
They did not disappear even after two coatings of the PCBM. The
sample shown in FIG. 12 has no spots. It is found out that
performing polishing makes it possible to remove the spots by the
second coating even though there exist spots on the surface after
the first coating. That is, it is possible to coat an exposed
portion of the active layer.
[0137] BCP was deposited on the substrate having had up to the PCBM
applied thereon by vacuum deposition. The PCBM layer and the BCP
layer function as the buffer layer functioning as the electron
transport layer. Then, an Ag layer as a second electrode was formed
on the buffer layer by a vacuum deposition method. Then, a heat
treatment was performed at 70.degree. C. and a photoelectric
conversion element of Example 1 was fabricated. In Example 1, the
conversion efficiency was measured while changing the heat
treatment time to zero minute, three minutes, 18 minutes, 33
minutes, 78 minutes, 93 minutes, and 285 minutes.
[0138] IV characteristics when a solar simulator irradiated each of
the photoelectric conversion elements with light of AM 1.5 under
the condition of 1000 W/m.sup.2 were measured. FIG. 13 is a chart
illustrating the IV characteristics of the photoelectric conversion
elements. Table 1 is a table illustrating relations between heat
treatment times and respective parameters (open-circuit voltage
V.sub.OC, short-circuit current density J.sub.SC, maximum output
Pmax, fill factor FF, conversion efficiency PCE, parallel
resistance Rsh, and interface resistance Rs). FIG. 14 is a chart
illustrating the conversion efficiency PCE, FIG. 15 is a chart
illustrating the relation with the open-circuit voltage V.sub.OC,
FIG. 16 is a chart illustrating the interface resistance Rs, FIG.
17 is a chart illustrating the fill factor FF, FIG. 18 is a chart
illustrating the short-circuit current density J.sub.SC, and FIG.
19 is a chart illustrating the parallel resistance Rsh. For
example, the sample with the conversion efficiency of 4.48%
improved as the heat treatment time elapsed, and reached about
twice the performance of the initial conversion efficiency, which
was 8.97% of the conversion efficiency. Further, J.sub.SC and FF
changed greatly as compared to V.sub.OC.
TABLE-US-00001 TABLE 1 TIME (min) 0 3 18 33 78 93 285 V.sub.OC (mV)
1006 1031 1031 1029 1011 1017 1010 Jsc (mA/cm.sup.2) 7.2 9.3 10.9
11.3 12.1 12.2 12.6 Pmax (mW) 4.48 4.93 6.92 7.28 8.22 8.19 8.97 FF
0.62 0.51 0.62 0.62 0.67 0.66 0.70 PCE (%) 4.48 4.93 6.92 7.28 8.22
8.19 8.97 Rsh (.OMEGA.) 664 588 926 1324 2129 1646 2977 Rs
(.OMEGA.) 20.6 30.4 16.8 16.6 11.6 13.0 9.5
[0139] Table 2 is a table illustrating reproducibility of the
respective parameters of the photoelectric conversion elements, and
FIG. 20 is a chart illustrating reproducibility of the respective
parameters of the photoelectric conversion elements. In Example 1,
samples A, B, and C were fabricated by the above-described steps
including the polishing step. Table 2 reveals that by performing
the polishing, a variation in conversion efficiency falls within a
range of 0.82 points within one batch. This makes it possible to
confirm that the photoelectric conversion element has high
reproducibility.
TABLE-US-00002 TABLE 2 SAMPLE No. A B C V.sub.OC(mV) 1022 1007 1031
Jsc(mA/cm.sup.2) 11.8 10.8 11.2 Pmax(mW) 7.81 6.92 7.15 FF 0.65
0.64 0.62 PCE(%) 7.81 6.92 7.15 Rsh(.OMEGA.) 2299 2028 1230
Rs(.OMEGA.) 12.3 13.3 19.9
Example 2
[0140] IV measurement and XRD measurement were performed on a
sample with the conversion efficiency of 9.1% that underwent up to
the polishing and the heat treatment by the steps similar to those
in Example 1 and a sample with the conversion efficiency of 7.1%
that did not undergo the polishing. A sample for the XRD
measurement was fabricated separately from the photoelectric
conversion element. The same manufacturing steps as those in
Example 1 were performed without deposition of BCP and Ag. Obtained
IV characteristics of the photoelectric conversion elements are
illustrated in FIG. 21, X-ray diffraction patterns are illustrated
in FIG. 22, and a partially enlarged view of FIG. 22 is illustrated
in FIG. 23 and FIG. 24. FIG. 23 and FIG. 24 reveal that by
performing the polishing, the diffraction pattern has a diffraction
peak of (004) of the perovskite compound. This diffraction peak is
detected by single crystal XRD, but is not easily detected in the
element. This is conceivably because by performing the polishing,
the crystal structure of the perovskite compound is once strained,
but is rearranged by the heat treatment or the like, and thereby an
ideal crystal structure from which effects of the deposition
process are eliminated is formed. At this time, the ratio of the
maximum intensity of the diffraction peak of (004) to the maximum
intensity of the diffraction peak of (220) was 0.18. It is possible
to say that as the intensity is higher, a more excellent crystal
can be obtained.
Example 3
[0141] Effects of the heat treatment were compared while changing
the direction of polishing. The operations were performed similarly
to Example 1 except the conditions of polishing, and a comparison
was made between a condition that the rolling shaft of the
polishing roller is vertical to the surface of the coating layer
and a condition that the rolling shaft of the polishing roller is
parallel to the surface of the coating layer. IV characteristics of
these are illustrated in FIG. 25 and FIG. 26. FIG. 25 is a chart
illustrating the IV characteristics of samples before the heat
treatment, and FIG. 26 is a chart illustrating the IV
characteristics of the samples after the heat treatment. As is
clear from FIG. 25, before the heat treatment, the conversion
efficiency is high under the vertical condition, but after the heat
treatment, the conversion efficiency is high under the parallel
condition. In FIG. 26, the conversion efficiency under the parallel
condition exceeded the conversion efficiency under the vertical
condition before the heat treatment. This is conceivably because
under the vertical condition, a separated perovskite compound
damaged a normal perovskite compound and the direction of load
applying to the coating layer was not a constant direction, thus
making it difficult to obtain a rearrangement effect of ions by the
heat treatment. It is conceived that under the parallel condition,
combining with a cleaning device such as a gas blow also enables
removal of the separated perovskite compound from the polished
surface and a load in a surface direction to apply to the coating
layer is also aligned in a constant direction, thus making it easy
to obtain the rearrangement effect.
Example 4
[0142] Effects of the heat treatment were compared while changing
the concentration of the precursor in the coating solution. The
same steps as those in Example 1 except the concentration of the
precursor were performed. IV characteristics of these are
illustrated in FIG. 27 to FIG. 29. As is clear from FIG. 27 to FIG.
29, even when the concentration of the precursor is increased to
1640 mg/ml and up to 1770 mg/ml, the effect by the heat treatment
appears. However, in the case of the concentration of the precursor
being 2020 mg/ml, the conversion efficiency does not improve even
after the heat treatment and the IV curve is not distinct. This is
conceivably because as the concentration of the precursor becomes
higher, the crystal grain diameter of the perovskite compound
becomes larger, and thus pin holes penetrating up to the
intermediate layer become likely to occur at the time of
polishing.
Comparative Example 1
[0143] Elements were fabricated by the same operations as those in
Example 1 except that the polishing was not performed, and IV
characteristics before and after the heat treatment at 70.degree.
C. were compared. As is clear from the IV characteristics
illustrated in FIG. 30, before and after the heat treatment, the
respective parameters constituting the IV characteristic change,
but the conversion efficiency hardly changes.
[0144] The above-described embodiments have been presented by way
of example only, and are not intended to limit the scope of the
inventions. Indeed, the novel embodiments described herein may be
embodied in a variety of other forms; furthermore, various
omissions, substitutions and changes in the form of the embodiments
described herein may be made without departing from the spirit of
the inventions. The accompanying claims and their equivalents are
intended to cover such forms or modifications as would fall within
the scope and spirit of the inventions.
[0145] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
methods described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the methods described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *